import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;

public class BinaryTree {

    static class TreeNode {
        public char val;
        public TreeNode left;//左孩子的引用
        public TreeNode right;//右孩子的引用

        public TreeNode(char val) {
            this.val = val;
        }
    }


    /**
     * 创建一棵二叉树 返回这棵树的根节点
     *
     * @return
     */
    public TreeNode createTree() {
        BinaryTree.TreeNode root = new BinaryTree.TreeNode('A');
        TreeNode node1 = new TreeNode('B');
        TreeNode node2 = new TreeNode('C');
        TreeNode node3 = new TreeNode('D');
        TreeNode node4 = new TreeNode('E');
        TreeNode node5 = new TreeNode('F');
        TreeNode node6 = new TreeNode('G');
        root.left = node1;
        root.right = node3;
        node1.right = node2;
        node3.left = node4;
        node3.right = node6;
        node4.right = node5;

        return root;
    }

    // 前序遍历
    public void preOrder(TreeNode root) {
        if(root == null) return;
        System.out.print(root.val + " ");
        preOrder(root.left);
        preOrder(root.right);
    }

    // 中序遍历
    void inOrder(TreeNode root) {
        if(root == null) return;
        inOrder(root.left);
        System.out.print(root.val + " ");
        inOrder(root.right);
    }

    // 后序遍历
    void postOrder(TreeNode root) {
        if(root == null) return;
        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val + " ");;
    }


    public static int nodeSize;
    /**
     * 获取树中节点的个数：遍历思路(前序遍历)
     */
    void size(TreeNode root) {
        if(root == null) return;

        nodeSize++;
        Stack<TreeNode> stack = new Stack<>();
        stack.push(root);
        root = root.left;
        while(root != null || !stack.empty()) {
            if(root != null) {
                nodeSize++;
                stack.push(root);
                root = root.left;
            }else {
                root = stack.pop().right;
            }
        }
    }

    /**
     * 获取节点的个数：子问题的思路
     *
     * @param root
     * @return
     */
    int size2(TreeNode root) {
        if(root == null) return 0;
        return 1 + size2(root.left) + size2(root.right);
    }


    /*
     获取叶子节点的个数：遍历思路
     */
    public static int leafSize = 0;

    void getLeafNodeCount1(TreeNode root) {
        if(root == null) return;

        Stack<TreeNode> stack = new Stack<>();
        stack.push(root);
        root = root.left;
        while(root != null || !stack.empty()) {
            if(root != null) {
                if(root.left == null && root.right == null) {
                    leafSize++;
                }
                stack.push(root);
                root = root.left;
            }else {
                TreeNode top = stack.pop();
                root = top.right;
            }
        }
    }

    /*
     获取叶子节点的个数：子问题(中序遍历递归)
     */
    int getLeafNodeCount2(TreeNode root) {
        if(root == null) return 0;
        if(root.left == null && root.right == null) {
            return 1;
        }
        return getLeafNodeCount2(root.left) + getLeafNodeCount2(root.right);
    }

    /*
    获取第K层节点的个数
     */
    int getKLevelNodeCount(TreeNode root, int k) {
        if(root == null || k <= 0) return 0;
        if(k == 1) return 1;

        return getKLevelNodeCount(root.left, k -1) + getKLevelNodeCount(root.right, k - 1);
    }

    /*
     获取二叉树的高度
     时间复杂度：O(N)
     */
    int getHeight(TreeNode root) {
        if(root == null) return 0;

        int leftHeight = getHeight(root.left);
        int rightHeight = getHeight(root.right);
        return leftHeight>rightHeight? leftHeight + 1 : rightHeight + 1;
    }


    // 检测值为value的元素是否存在
    public boolean find(TreeNode root, char val) {
        if(root == null) return false;
        if(root.val == val) return  true;

        boolean leftTree = find(root.left, val);
        boolean rightTree = find(root.right, val);
        return leftTree || rightTree;
    }

    //层序遍历
    void levelOrder(TreeNode root) {
        if(root == null) return;;

        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while(!queue.isEmpty()) {
            root = queue.poll();
            System.out.print(root.val + " ");
            if(root.left != null) queue.offer(root.left);
            if(root.right != null) queue.offer(root.right);
        }
        System.out.println();
    }


    // 判断一棵树是不是完全二叉树
    boolean isCompleteTree(TreeNode root) {
        if(root == null) return true;

        if(root.left == null && root.right != null) {
            return false;
        }
        boolean leftTree = isCompleteTree(root.left);
        boolean rightTree = isCompleteTree(root.right);
        return leftTree && rightTree;
    }

}
